a
reference to the ancient
calendar devised and used by the
Romans. Very early in their
history, the
Romans began basing their
calendar on the idea that 12 lunar months make a year. Each lunar month (from new moon to new moon) is about 29 1/2 days, so the Roman year came to 354 days. But the true solar year (the
time it takes the Earth to circle the
sun) is just under 365 1/4 days. The
Romans made up for the difference by adding an extra month every few years.
—SHSBC Binder 22 Approved Glossary